Cellular phones are continuously being reduced in size to enhance portability. For example, today's smallest available cellular phone device can conveniently fit in a person's pocket or clip easily onto a belt. The limit in size appears to be a cellular phone having dimensions similar or even smaller than those of a credit card so that it will fit in a wallet.
So much emphasis has been placed on reducing cell phone size that antenna gains of corresponding cell phone antennas are surprisingly poor. Typically, antenna gains of smaller cellular phones are −3 dBi or even lower. Antennas used in these phones, therefore, generally do not have the ability to mitigate the effects of interference or reduce fading. Consequently, the quality of communication can suffer as a result of reduced cell phone size.
U.S. Pat. No. 5,905,473 discloses an adjustable antenna having an active antenna element and multiple passive antenna elements that reflect RF energy. Control of the passive elements is achieved using switches and various selectable impedance elements. A portion of the re-radiated energy from the passive elements is picked up by the active antenna, and the phase with which the re-radiated energy is received by the active antenna is controllable.